Producing alumina



atented June 20, 1944 7 2,351,941 raonuome ALUMINA Walter Dyckerhoif, Mainz-Amoneburg, and Wilhelm Wittekindt, Wiesbaden-Biebrlch, Germany; vested in the Alien Property Custodian No Drawing. Application April 29, 1941, Serial No. 391,007. In Germany April 20, 1940 3 Claims. (Cl. 23-443) This invention relates to improvements in the of silicic acid, it has proved preferable to effect reduction of alumina from aluminous raw mathe lixiviation at first in presence ofan excess erials. of the material to be lixiviated.

One has already proposed to recover alumina The invention will now be more fully explained y heating such raw material with lime to soluwith reference to a numerical example of exec-uilize or open it, and dissolving the resulting tion: alcium aluminates by lixiviating the opened ma- 100 kilograms of a raw aluminous material erial with soda solution. This mode of operatcontaining 25% of A1202 are intimately mixed 'ng presents the important draw-back that bewith about 150 kilograms of carbonate of lime ides the alumina a considerable amount of silicic l containing96% of CaCOa and the whole is subacid is dissolved which on working up the solujected to a calcining process at temperatures of ion is precipitated together with the alumina from 1000 to 1450" C. The calcined product is and prohibits the immediate use of .the alumina then lixiviated with a soda solution containing hus obtained for a number/of purposes, especlalabout 5 grams sodium carbonate per liter. About y for producing aluminum. Therefore one has to grams of fresh material besides 60 to 200 preferred to lixiviate the calcined product with grams of already lixiviated material from former water alone instead of soda solution. Calcium operations should be used per each liter of solualum-inates being soluble in water only to a small tion. The resulting solution contains about 2 extent, considerable quantities of liquid are rev grams of alumina per liter and is practically free quired for this purpose, and as a rule solutions 20 from silicic acid. By analysis we have tested containing only 1 g. A1203 per liter are obtained. that this solution contains about 0.02 to 0.06% Even when employing a diluted soda solution con- SiOz, calculated upon the A1203 content. The taini-ng less than 1 g. NazCOa per liter still conaluminous solution thus obtained may then be siderablequantities of liquid vare needed, altreated in the well-known manner, for obtainthough the solutions do not contain notable per- 25 ing pure alumina. e. g. by precipitating it with centages of SlOz. carbon dioxide.

Now we have found the surprising fact that 8. Instead of soda solution any other alkaline solution with higher alkali metal carbonate coi'lsolution, for instance, caustic soda or potash tents may be employed if in the lixiviating opsolution may be employed for lixiviating the cal eration greater amounts of lixiviated material 39 cined product. Likewise in the calcining" are present besides the calcined product. It apoperation an alkaline earth other than lime may pears that the SiOz contents, at first present in be used. the lixiviating liquid, practically disappear with We claim: the progressive enrichment of the solution with. 1. The process of recovering alumina from lixiviaiied material- Contrary to What a man aluminous raw materials which comprises mixskilled in the art could expect, the silicious resi ing the raw materials with an alkaline earth, due freed from alumina counteracts the dissolucalcining th i tu lixivi tin the calcined tion of silicic acid or precipitates the silicic acid product with alkali metal carbonate solution in already dissolved. presence of a considerable amount of a similar Therefore process affords the 40 product btained from a forn er operation 31.. of employing a Silicious lime in Order to bind the ready'lixiviated and consisting largely of silica excess of carbonic acid. when the alkali metal residue, and precipitating alumina f th carbonate solution resulting from the circulation sulting alkali m t l l in te solution, is utilised, which solution after the precipitation 2, Th process of recovering alumina from of the alumina still contains considerable quanalumipous raw materials which comprises tities of carbonic acid, because even with higher m th raw t i l with an alkaline earth, silicic acid content of such solution the dissolved calcining the mixture, lixiviating one part by amount of silicic a d is again P p a ed in weight of the calcined product with alkali metals th l l s process. Hereby th economy of carbonate solution in presence of three to six t e p c s is dera y p oved, owing to 59 parts by weight of the calcined product obtained the fact that now for neutralizing the solutions from a former operation, already lixiviated and obtained from the carbon dioxide saturator we consisting largely of silica residue, and precipi-' are no more obliged to rely upon the use of the .t ting. lu i from th resulting alkali met l purest lime. In order to avoid, in the beginning 'aluminate s mti 0f t P e the dissolution of g eater unts The process of recovering alumina from aluminous raw materials which comprises mixing the raw materials with lime, calcining the mixture, lixiviating the calcined product with alkali metal carbonate solution in presence of a considerable amount of a similar. product. ob-

tained from a former operation, already lixiviated and consisting largely of silica residue, introducing carbon dioxide into the resulting alkali metal aluminate solution, thereby precipitating alumina, treating the resulting alkali metal bicarbonate solution with silicious lime to remove its excess of carbon dioxide, and repeating the process with the resulting alkali metal carbonate solution.

' WAL DYCKERHOFF. 

